Krill are small crustaceans of the orderEuphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian word krill, meaning "small fry of fish", which is also often attributed to species of fish.
Krill are considered an important trophic level connection – near the bottom of the food chain. They feed on phytoplankton and (to a lesser extent) zooplankton, yet also are the main source of food for many larger animals. In the Southern Ocean, one species, the Antarctic krill, Euphausia superba, makes up an estimated biomass of around 379,000,000 tonnes, making it among the species with the largest total biomass. Over half of this biomass is eaten by whales, seals, penguins, squid, and fish each year. Most krill species display large daily vertical migrations, thus providing food for predators near the surface at night and in deeper waters during the day.
Krill are fished commercially in the Southern Ocean and in the waters around Japan. The total global harvest amounts to 150,000–200,000 tonnes annually, most of this from the Scotia Sea. Most of the krill catch is used for aquaculture and aquarium feeds, as bait in sport fishing, or in the pharmaceutical industry. In Japan, the Philippines, and Russia, krill are also used for human consumption and are known as okiami (オキアミ) in Japan. They are eaten as camarones in Spain and Philippines. In the Philippines, krill are also known as alamang and are used to make a salty paste called bagoong.
Phylogeny obtained from morphological data, (♠) names coined in, (♣) possibly paraphyletic taxon due to Nematobrachion in. (♦) clades differs from Casanova (1984), where Pseudoeuphausia is sister to Nyctiphanes, Euphausia is sister to Thysanopoda and Nematobrachion is sister to Stylocheiron.
As of 2013[update], the order Euphausiacea is believed to be monophyletic due to several unique conserved morphological characteristics (autapomorphy) such as its naked filamentous gills and thin thoracopods and by molecular studies.
There have been many theories of the location of the order Euphausiacea. Since the first description of Thysanopode tricuspide by Henri Milne-Edwards in 1830, the similarity of their biramous thoracopods had led zoologists to group euphausiids and Mysidacea in the order Schizopoda, which was split by Johan Erik Vesti Boas in 1883 into two separate orders. Later, William Thomas Calman (1904) ranked the Mysidacea in the superorder Peracarida and euphausiids in the superorder Eucarida, although even up to the 1930s the order Schizopoda was advocated. It was later also proposed that order Euphausiacea should be grouped with the Penaeidae (family of prawns) in the Decapoda based on developmental similarities, as noted by Robert Gurney and Isabella Gordon. The reason for this debate is that krill share some morphological features of decapods and others of mysids.
Molecular studies have not unambiguously grouped them, possibly due to the paucity of key rare species such as Bentheuphausia amblyops in krill and Amphionides reynaudii in Eucarida. One study supports the monophyly of Eucarida (with basal Mysida), another groups Euphausiacea with Mysida (the Schizopoda), while yet another groups Euphausiacea with Hoplocarida.
No extant fossil can be unequivocally assigned to Euphausiacea. Some extinct eumalacostracantaxa have been thought to be euphausiaceans such as Anthracophausia, Crangopsis – now assigned to the Aeschronectida (Hoplocarida) – and Palaeomysis. All dating of speciation events were estimated by molecular clock methods, which placed the last common ancestor of the krill family Euphausiidae (order Euphausiacea minus Bentheuphausia amblyops) to have lived in the Lower Cretaceous about 130 million years ago.
Species with endemic distributions include Nyctiphanes capensis, which occurs only in the Benguela current,E. mucronata in the Humboldt current, and the six Euphausia species native to the Southern Ocean.
In the Antarctic, seven species are known, one in genus Thysanoessa (T. macrura) and six in Euphausia. The Antarctic krill (Euphausia superba) commonly lives at depths reaching 100 m (330 ft), whereas ice krill (Euphausia crystallorophias) reach depth of 4,000 m (13,100 ft), though they commonly inhabit depths of at most 300–600 m (1,000–2,000 ft). Both are found at latitudes south of 55° S, with E. crystallorophias dominating south of 74° S and in regions of pack ice. Other species known in the Southern Ocean are E. frigida, E. longirostris, E. triacantha and E. vallentini.
Krill feature intricate compound eyes. Some species adapt to different lighting conditions through the use of screening pigments.
They have two antennae and several pairs of thoracic legs called pereiopods or thoracopods, so named because they are attached to the thorax. Their number varies among genera and species. These thoracic legs include feeding legs and grooming legs.
Most krill are about 1–2 centimetres (0.4–0.8 in) long as adults. A few species grow to sizes on the order of 6–15 centimetres (2.4–5.9 in). The largest krill species, Thysanopoda spinicauda, lives deep in the open ocean. Krill can be easily distinguished from other crustaceans such as true shrimp by their externally visible gills.
Except for Bentheuphausia amblyops, krill are bioluminescent animals having organs called photophores that can emit light. The light is generated by an enzyme-catalysed chemiluminescence reaction, wherein a luciferin (a kind of pigment) is activated by a luciferase enzyme. Studies indicate that the luciferin of many krill species is a fluorescenttetrapyrrole similar but not identical to dinoflagellate luciferin and that the krill probably do not produce this substance themselves but acquire it as part of their diet, which contains dinoflagellates. Krill photophores are complex organs with lenses and focusing abilities, and can be rotated by muscles. The precise function of these organs is as yet unknown; possibilities include mating, social interaction or orientation and as a form of counter-illumination camouflage to compensate their shadow against overhead ambient light.
Processes in the biological pump
Phytoplankton convert CO2, which has dissolved from the atmosphere into the surface oceans (90 Gt yr−1) into particulate organic carbon (POC) during primary production (~ 50 Gt C yr−1). Phytoplankton are then consumed by krill and small zooplankton grazers, which in turn are preyed upon by higher trophic levels. Any unconsumed phytoplankton form aggregates, and along with zooplankton faecal pellets, sink rapidly and are exported out of the mixed layer (< 12 Gt C yr−1 14). Krill, zooplankton and microbes intercept phytoplankton in the surface ocean and sinking detrital particles at depth, consuming and respiring this POC to CO2 (dissolved inorganic carbon, DIC), such that only a small proportion of surface-produced carbon sinks to the deep ocean (i.e., depths > 1000 m). As krill and smaller zooplankton feed, they also physically fragment particles into small, slower- or non-sinking pieces (via sloppy feeding, coprorhexy if fragmenting faeces), retarding POC export. This releases dissolved organic carbon (DOC) either directly from cells or indirectly via bacterial solubilisation (yellow circle around DOC). Bacteria can then remineralise the DOC to DIC (CO2, microbial gardening). Diel vertically migrating krill, smaller zooplankton and fish can actively transport carbon to depth by consuming POC in the surface layer at night, and metabolising it at their daytime, mesopelagic residence depths. Depending on species life history, active transport may occur on a seasonal basis as well. Numbers given are carbon fluxes (Gt C yr−1) in white boxes and carbon masses (Gt C) in dark boxes.
Krill are an important element of the aquatic food chain. Krill convert the primary production of their prey into a form suitable for consumption by larger animals that cannot feed directly on the minuscule algae. Northern krill and some other species have a relatively small filtering basket and actively hunt copepods and larger zooplankton.
Disturbances of an ecosystem resulting in a decline in the krill population can have far-reaching effects. During a coccolithophore bloom in the Bering Sea in 1998, for instance, the diatom concentration dropped in the affected area. Krill cannot feed on the smaller coccolithophores, and consequently the krill population (mainly E. pacifica) in that region declined sharply. This in turn affected other species: the shearwater population dropped. The incident was thought to have been one reason salmon did not spawn that season.
Several single-celled endoparasitoidicciliates of the genus Collinia can infect species of krill and devastate affected populations. Such diseases were reported for Thysanoessa inermis in the Bering Sea and also for E. pacifica, Thysanoessa spinifera, and T. gregaria off the North American Pacific coast. Some ectoparasites of the family Dajidae (epicaridean isopods) afflict krill (and also shrimp and mysids); one such parasite is Oculophryxus bicaulis, which was found on the krill Stylocheiron affine and S. longicorne. It attaches itself to the animal's eyestalk and sucks blood from its head; it apparently inhibits the host's reproduction, as none of the afflicted animals reached maturity.
The life cycle of krill is relatively well understood, despite minor variations in detail from species to species. After krill hatch, they experience several larval stages—nauplius, pseudometanauplius, metanauplius, calyptopsis, and furcilia, each of which divides into sub-stages. The pseudometanauplius stage is exclusive to species that lay their eggs within an ovigerous sac: so-called "sac-spawners". The larvae grow and moult repeatedly as they develop, replacing their rigid exoskeleton when it becomes too small. Smaller animals moult more frequently than larger ones. Yolk reserves within their body nourish the larvae through metanauplius stage.
By the calyptopsis stages differentiation has progressed far enough for them to develop a mouth and a digestive tract, and they begin to eat phytoplankton. By that time their yolk reserves are exhausted and the larvae must have reached the photic zone, the upper layers of the ocean where algae flourish. During the furcilia stages, segments with pairs of swimmerets are added, beginning at the frontmost segments. Each new pair becomes functional only at the next moult. The number of segments added during any one of the furcilia stages may vary even within one species depending on environmental conditions. After the final furcilia stage, an immature juvenile emerges in a shape similar to an adult, and subsequently develops gonads and matures sexually.
The head of a female krill of the sac-spawning species Nematoscelis difficilis with her brood sac. The eggs have a diameter of 0.3–0.4 millimetres (0.012–0.016 in)
During the mating season, which varies by species and climate, the male deposits a sperm sack at the female's genital opening (named thelycum). The females can carry several thousand eggs in their ovary, which may then account for as much as one third of the animal's body mass. Krill can have multiple broods in one season, with interbrood intervals lasting on the order of days.
Krill employ two types of spawning mechanism. The 57 species of the genera Bentheuphausia, Euphausia, Meganyctiphanes, Thysanoessa, and Thysanopoda are "broadcast spawners": the female releases the fertilised eggs into the water, where they usually sink, disperse, and are on their own. These species generally hatch in the nauplius 1 stage, but have recently been discovered to hatch sometimes as metanauplius or even as calyptopis stages. The remaining 29 species of the other genera are "sac spawners", where the female carries the eggs with her, attached to the rearmost pairs of thoracopods until they hatch as metanauplii, although some species like Nematoscelis difficilis may hatch as nauplius or pseudometanauplius.
Moulting occurs whenever a specimen outgrows its rigid exoskeleton. Young animals, growing faster, moult more often than older and larger ones. The frequency of moulting varies widely by species and is, even within one species, subject to many external factors such as latitude, water temperature, and food availability. The subtropical species Nyctiphanes simplex, for instance, has an overall inter-moult period of two to seven days: larvae moult on the average every four days, while juveniles and adults do so, on average, every six days. For E. superba in the Antarctic sea, inter-moult periods ranging between 9 and 28 days depending on the temperature between −1 and 4 °C (30 and 39 °F) have been observed, and for Meganyctiphanes norvegica in the North Sea the inter-moult periods range also from 9 and 28 days but at temperatures between 2.5 and 15 °C (36.5 and 59.0 °F).E. superba is able to reduce its body size when there is not enough food available, moulting also when its exoskeleton becomes too large. Similar shrinkage has also been observed for E. pacifica, a species occurring in the Pacific Ocean from polar to temperate zones, as an adaptation to abnormally high water temperatures. Shrinkage has been postulated for other temperate-zone species of krill as well.
Some high-latitude species of krill can live for more than six years (e.g., Euphausia superba); others, such as the mid-latitude species Euphausia pacifica, live for only two years. Subtropical or tropical species' longevity is still shorter, e.g., Nyctiphanes simplex, which usually lives for only six to eight months.
A krill swarm
Most krill are swarming animals; the sizes and densities of such swarms vary by species and region. For Euphausia superba, swarms reach 10,000 to 60,000 individuals per cubic meter. Swarming is a defensive mechanism, confusing smaller predators that would like to pick out individuals. In 2012, Gandomi and Alavi presented what appears to be a successful stochastic algorithm for modelling the behaviour of krill swarms. The algorithm is based on three main factors: " (i) movement induced by the presence of other individuals (ii) foraging activity, and (iii) random diffusion."
Krill typically follow a diurnalvertical migration. It has been assumed that they spend the day at greater depths and rise during the night toward the surface. The deeper they go, the more they reduce their activity, apparently to reduce encounters with predators and to conserve energy. Swimming activity in krill varies with stomach fullness. Sated animals that had been feeding at the surface swim less actively and therefore sink below the mixed layer. As they sink they produce feces which implies a role in the Antarctic carbon cycle. Krill with empty stomachs swim more actively and thus head towards the surface.
Vertical migration may be a 2–3 times daily occurrence. Some species (e.g., Euphausia superba, E. pacifica, E. hanseni, Pseudeuphausia latifrons, and Thysanoessa spinifera) form surface swarms during the day for feeding and reproductive purposes even though such behaviour is dangerous because it makes them extremely vulnerable to predators.
Experimental studies using Artemia salina as a model suggest that the vertical migrations of krill several hundreds of metres, in groups tens of metres deep, could collectively create enough downward jets of water to have a significant effect on ocean mixing.
Dense swarms can elicit a feeding frenzy among fish, birds and mammal predators, especially near the surface. When disturbed, a swarm scatters, and some individuals have even been observed to moult instantaneously, leaving the exuvia behind as a decoy.
Krill normally swim at a pace of 5–10 cm/s (2–3 body lengths per second), using their swimmerets for propulsion. Their larger migrations are subject to ocean currents. When in danger, they show an escape reaction called lobstering – flicking their caudal structures, the telson and the uropods, they move backwards through the water relatively quickly, achieving speeds in the range of 10 to 27 body lengths per second, which for large krill such as E. superba means around 0.8 m/s (3 ft/s). Their swimming performance has led many researchers to classify adult krill as micro-nektonic life-forms, i.e., small animals capable of individual motion against (weak) currents. Larval forms of krill are generally considered zooplankton.
Role of Antarctic krill in biogeochemical cycles
Krill (as swarms and individuals) feed on phytoplankton at the surface (1) leaving only a proportion to sink as phytodetrital aggregates (2), which are broken up easily and may not sink below the permanent thermocline. Krill also release faecal pellets (3) whilst they feed, which can sink to the deep sea but can be consumed (coprophagy) and degraded as they descend (4) by krill, bacteria and zooplankton. In the marginal ice zone, faecal pellet flux can reach greater depths (5). Krill also release moults, which sink and contribute to the carbon flux (6). Nutrients are released by krill during sloppy feeding, excretion and egestion, such as iron and ammonium (7, see Fig. 2 for other nutrients released), and if they are released near the surface can stimulate phytoplankton production and further atmospheric CO2 drawdown. Some adult krill permanently reside deeper in the water column, consuming organic material at depth (8). Any carbon (as organic matter or as CO2) that sinks below the permanent thermocline is removed from subjection to seasonal mixing and will remain stored in the deep ocean for at least a year (9). The swimming motions of migrating adult krill that migrate can mix nutrient-rich water from the deep (10), further stimulating primary production. Other adult krill forage on the seafloor, releasing respired CO2 at depth and may be consumed by demersal predators (11). Larval krill, which in the Southern Ocean reside under the sea ice, undergo extensive diurnal vertical migration (12), potentially transferring CO2 below the permanent thermocline. Krill are consumed by many predators including baleen whales (13), leading to storage of some of the krill carbon as biomass for decades before the whale dies, sinks to the seafloor and is consumed by deep sea organisms.
When krill moult they release dissolved calcium, fluoride and phosphorus from the exoskeleton (1). The chitin (organic material) that forms the exoskeleton contributes to organic particle flux sinking to the deep ocean. Krill respire a portion of the energy derived from consuming phytoplankton or other animals as carbon dioxide (2), when swimming from mid/deep waters to the surface in large swarms krill mix water, which potentially brings nutrients to nutrient-poor surface waters (3), ammonium and phosphate is released from the gills and when excreting, along with dissolved organic carbon, nitrogen (e.g., urea) and phosphorus (DOC, DON and DOP, 2 & 4). Krill release fast-sinking faecal pellets containing particulate organic carbon, nitrogen and phosphorus (POC, PON and POP) and iron, the latter of which is bioavailable when leached into surrounding waters along with DOC, DON and DOP (5).
Deep frozen plates of Antarctic krill for use as animal feed and raw material for cooking
Krill have been harvested as a food source for humans and domesticated animals since at least the 19th century, and possibly earlier in Japan, where it was known as okiami. Large-scale fishing developed in the late 1960s and early 1970s, and now occurs only in Antarctic waters and in the seas around Japan. Historically, the largest krill fishery nations were Japan and the Soviet Union, or, after the latter's dissolution, Russia and Ukraine. The harvest peaked, which in 1983 was about 528,000 tonnes in the Southern Ocean alone (of which the Soviet Union took in 93%), is now managed as a precaution against overfishing.
The annual Antarctic catch stabilised at around 100,000 tonnes, which is roughly one fiftieth of the CCAMLR catch quota. The main limiting factor was probably high costs along with political and legal issues. The Japanese fishery saturated at some 70,000 tonnes.
Although krill are found worldwide, fishing in Southern Oceans are preferred because the krill are more "catchable" and abundant in these regions. Particularly in Antarctic seas which are considered as pristine, they are considered a "clean product".
In 2018 it was announced that almost every krill fishing company operating in Antarctica will abandon operations in huge areas around the Antarctic Peninsula from 2020, including "buffer zones" around breeding colonies of penguins.
Although the total biomass of Antarctic krill may be as abundant as 400 million tonnes, the human impact on this keystone species is growing, with a 39% increase in total fishing yield to 294,000 tonnes over 2010–2014. Major countries involved in krill harvesting are Norway (56% of total catch in 2014), the Republic of Korea (19%), and China (18%).
^"Krill". Online Etymology Dictionary. Retrieved June 22, 2010.
^A. Atkinson; V. Siegel; E.A. Pakhomov; M.J. Jessopp; V. Loeb (2009). "A re-appraisal of the total biomass and annual production of Antarctic krill" (PDF). Deep-Sea Research Part I. 56 (5): 727–740. Bibcode:2009DSRI...56..727A. doi:10.1016/j.dsr.2008.12.007.
^E. Brinton (1962). "The distribution of Pacific euphausiids". Bull. Scripps Inst. Oceanogr. 8 (2): 51–270.
^ abS. Nicol; Y. Endo (1999). "Krill fisheries: Development, management and ecosystem implications". Aquatic Living Resources. 12 (2): 105–120. doi:10.1016/S0990-7440(99)80020-5.
^ abcdAndreas Maas; Dieter Waloszek (2001). "Larval development of Euphausia superba Dana, 1852 and a phylogenetic analysis of the Euphausiacea" (PDF). Hydrobiologia. 448: 143–169. doi:10.1023/A:1017549321961. S2CID 32997380. Archived from the original (PDF) on 2011-07-18.
^ abcBernadette Casanova (2003). "Ordre des Euphausiacea Dana, 1852". Crustaceana. 76 (9): 1083–1121. doi:10.1163/156854003322753439. JSTOR 20105650.
^M. Eugenia D'Amato; Gordon W. Harkins; Tulio de Oliveira; Peter R. Teske; Mark J. Gibbons (2008). "Molecular dating and biogeography of the neritic krill Nyctiphanes" (PDF). Marine Biology. 155 (2): 243–247. doi:10.1007/s00227-008-1005-0. S2CID 17750015.
^Xin Shen; Haiqing Wang; Minxiao Wang; Bin Liu (2011). "The complete mitochondrial genome sequence of Euphausia pacifica (Malacostraca: Euphausiacea) reveals a novel gene order and unusual tandem repeats". Genome. 54 (11): 911–922. doi:10.1139/g11-053. PMID22017501.
^Johan Erik Vesti Boas (1883). "Studien über die Verwandtschaftsbeziehungen der Malacostraken" [Studies on the relationships of the Malacostraca]. Morphologisches Jahrbuch (in German). 8: 485–579.
^Trisha Spears, Ronald W. DeBry, Lawrence G. Abele & Katarzyna Chodyl (2005). Boyko, Christopher B. (ed.). "Peracarid monophyly and interordinal phylogeny inferred from nuclear small-subunit ribosomal DNA sequences (Crustacea: Malacostraca: Peracarida)" (PDF). Proceedings of the Biological Society of Washington. 118 (1): 117–157. doi:10.2988/0006-324X(2005)118[117:PMAIPI]2.0.CO;2.CS1 maint: multiple names: authors list (link)
^J. J. Torres; J. J. Childress (1985). "Respiration and chemical composition of the bathypelagic euphausiid Bentheuphausia amblyops". Marine Biology. 87 (3): 267–272. doi:10.1007/BF00397804. S2CID 84486097.
^ abcJ. Mauchline; L. R. Fisher (1969). The Biology of Euphausiids. Advances in Marine Biology. 7. Academic Press. ISBN 978-7-7708-3615-2.
^ abcJaime Gómez-Gutiérrez; Carlos J. Robinson (2005). "Embryonic, early larval development time, hatching mechanism and interbrood period of the sac-spawning euphausiid Nyctiphanes simplex Hansen". Journal of Plankton Research. 27 (3): 279–295. doi:10.1093/plankt/fbi003.
^S. N. Jarman; N. G. Elliott; S. Nicol; A. McMinn (2002). "Genetic differentiation in the Antarctic coastal krill Euphausia crystallorophias". Heredity. 88 (4): 280–287. doi:10.1038/sj.hdy.6800041. PMID11920136.
^R. Escribano; V. Marin; C. Irribarren (2000). "Distribution of Euphausia mucronata at the upwelling area of Peninsula Mejillones, northern Chile: the influence of the oxygen minimum layer". Scientia Marina. 64 (1): 69–77. doi:10.3989/scimar.2000.64n169.
^"Krill, Euphausia superba". MarineBio.org. Retrieved February 25, 2009.
^J. A. Kirkwood (1984). "A Guide to the Euphausiacea of the Southern Ocean". ANARE Research Notes. 1: 1–45.
^A. Sala; M. Azzali; A. Russo (2002). "Krill of the Ross Sea: distribution, abundance and demography of Euphausia superba and Euphausia crystallorophias during the Italian Antarctic Expedition (January–February 2000)". Scientia Marina. 66 (2): 123–133. doi:10.3989/scimar.2002.66n2123.
^G. W. Hosie; M. Fukuchi; S. Kawaguchi (2003). "Development of the Southern Ocean Continuous Plankton Recorder survey" (PDF). Progress in Oceanography. 58 (2–4): 263–283. Bibcode:2003PrOce..58..263H. doi:10.1016/j.pocean.2003.08.007.[permanent dead link]
^E. Gaten. "Meganyctiphanes norvegica". University of Leicester. Archived from the original on July 1, 2009. Retrieved February 25, 2009.
^E. Brinton (1953). "Thysanopoda spinicauda, a new bathypelagic giant euphausiid crustacean, with comparative notes on T. cornuta and T. egregia". Journal of the Washington Academy of Sciences. 43: 408–412.
^"Euphausiacea". Tasmanian Aquaculture & Fisheries Institute. Archived from the original on September 30, 2009. Retrieved June 6, 2010.
^O. Shimomura (1995). "The roles of the two highly unstable components F and P involved in the bioluminescence of euphausiid shrimps". Journal of Bioluminescence and Chemiluminescence. 10 (2): 91–101. doi:10.1002/bio.1170100205. PMID7676855.
^P. J. Herring; E. A. Widder (2001). "Bioluminescence in Plankton and Nekton". In J. H. Steele; S. A. Thorpe; K. K. Turekian (eds.). Encyclopedia of Ocean Science. 1. Academic Press, San Diego. pp. 308–317. ISBN 978-0-12-227430-5.
^S. M. Lindsay; M. I. Latz (1999). Experimental evidence for luminescent countershading by some euphausiid crustaceans. American Society of Limnology and Oceanography (ASLO) Aquatic Sciences Meeting. Santa Fe.
^ abcdCavan, E.L., Belcher, A., Atkinson, A., Hill, S.L., Kawaguchi, S., McCormack, S., Meyer, B., Nicol, S., Ratnarajah, L., Schmidt, K. and Steinberg, D.K. (2019) "The importance of Antarctic krill in biogeochemical cycles". Nature communications, 10(1): 1–13. doi:10.1038/s41467-019-12668-7. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
^G. C. Cripps; A. Atkinson (2000). "Fatty acid composition as an indicator of carnivory in Antarctic krill, Euphausia superba". Canadian Journal of Fisheries and Aquatic Sciences. 57 (S3): 31–37. doi:10.1139/f00-167.
^M. J. Schramm (October 10, 2007). "Tiny Krill: Giants in Marine Food Chain". NOAA National Marine Sanctuary Program. Retrieved June 4, 2010.
^J. Weier (1999). "Changing currents color the Bering Sea a new shade of blue". NOAA Earth Observatory. Retrieved June 15, 2005.
^R. D. Brodeur; G. H. Kruse; P. A. Livingston; G. Walters; J. Ianelli; G. L. Swartzman; M. Stepanenko; T. Wyllie-Echeverria (1998). Draft Report of the FOCI International Workshop on Recent Conditions in the Bering Sea. NOAA. pp. 22–26.
^J. Gómez-Gutiérrez; W. T. Peterson; A. de Robertis; R. D. Brodeur (2003). "Mass mortality of krill caused by parasitoid ciliates". Science. 301 (5631): 339. doi:10.1126/science.1085164. PMID12869754. S2CID 28471713.
^J. D. Shields; J. Gómez-Gutiérrez (1996). "Oculophryxus bicaulis, a new genus and species of dajid isopod parasitic on the euphausiid Stylocheiron affine Hansen". International Journal for Parasitology. 26 (3): 261–268. doi:10.1016/0020-7519(95)00126-3. PMID8786215.
^R. M. Ross; L. B. Quetin (1986). "How productive are Antarctic krill?". BioScience. 36 (4): 264–269. doi:10.2307/1310217. JSTOR 1310217.
^Janine Cuzin-Roudy (2000). "Seasonal reproduction, multiple spawning, and fecundity in northern krill, Meganyctiphanes norvegica, and Antarctic krill, Euphausia superba". Canadian Journal of Fisheries and Aquatic Sciences. 57 (S3): 6–15. doi:10.1139/f00-165.
^J. Gómez-Gutiérrez (2002). "Hatching mechanism and delayed hatching of the eggs of three broadcast spawning euphausiid species under laboratory conditions". Journal of Plankton Research. 24 (12): 1265–1276. doi:10.1093/plankt/24.12.1265.
^E. Brinton; M. D. Ohman; A. W. Townsend; M. D. Knight; A. L. Bridgeman (2000). Euphausiids of the World Ocean. World Biodiversity Database CD-ROM Series, Springer Verlag. ISBN 978-3-540-14673-5.
^F. Buchholz (2003). "Experiments on the physiology of Southern and Northern krill, Euphausia superba and Meganyctiphanes norvegica, with emphasis on moult and growth – a review". Marine and Freshwater Behaviour and Physiology. 36 (4): 229–247. doi:10.1080/10236240310001623376. S2CID 85121989.
^H.-C. Shin; S. Nicol (2002). "Using the relationship between eye diameter and body length to detect the effects of long-term starvation on Antarctic krill Euphausia superba". Marine Ecology Progress Series. 239: 157–167. Bibcode:2002MEPS..239..157S. doi:10.3354/meps239157.
^B. Marinovic; M. Mangel (1999). "Krill can shrink as an ecological adaptation to temporarily unfavourable environments" (PDF). Ecology Letters. 2: 338–343.
^J. G. Gómez (1995). "Distribution patterns, abundance and population dynamics of the euphausiidsNyctiphanes simplex and Euphausia eximia off the west coast of Baja California, Mexico" (PDF). Marine Ecology Progress Series. 119: 63–76. Bibcode:1995MEPS..119...63G. doi:10.3354/meps119063.
^U. Kils; P. Marshall (1995). "Der Krill, wie er schwimmt und frisst – neue Einsichten mit neuen Methoden ("The Antarctic krill – how it swims and feeds – new insights with new methods")". In I. Hempel; G. Hempel (eds.). Biologie der Polarmeere – Erlebnisse und Ergebnisse (Biology of the Polar Oceans Experiences and Results). Fischer Verlag. pp. 201–210. ISBN 978-3-334-60950-7.
^R. Piper (2007). Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals. Greenwood Press. ISBN 978-0-313-33922-6.
^Gandomi, A.H.; Alavi, A.H. (2012). "Krill Herd: A New Bio-Inspired Optimization Algorithm". Communications in Nonlinear Science and Numerical Simulation. 17 (12): 4831–4845. Bibcode:2012CNSNS..17.4831G. doi:10.1016/j.cnsns.2012.05.010.
^J. S. Jaffe; M. D. Ohmann; A. de Robertis (1999). "Sonar estimates of daytime activity levels of Euphausia pacifica in Saanich Inlet" (PDF). Canadian Journal of Fisheries and Aquatic Sciences. 56 (11): 2000–2010. doi:10.1139/cjfas-56-11-2000. Archived from the original (PDF) on 2011-07-20.
^Geraint A. Tarling; Magnus L. Johnson (2006). "Satiation gives krill that sinking feeling". Current Biology. 16 (3): 83–84. doi:10.1016/j.cub.2006.01.044. PMID16461267.
^Dan Howard (2001). "Krill" (PDF). In Herman A. Karl; John L. Chin; Edward Ueber; Peter H. Stauffer; James W. Hendley II (eds.). Beyond the Golden Gate – Oceanography, Geology, Biology, and Environmental Issues in the Gulf of the Farallones. United States Geological Survey. pp. 133–140. Circular 1198. Retrieved October 8, 2011.
^Wishart, Skye (July–August 2018). "The krill effect". New Zealand Geographic (152): 24.
^David A. Demer; Stéphane G. Conti (2005). "New target-strength model indicates more krill in the Southern Ocean". ICES Journal of Marine Science. 62 (1): 25–32. doi:10.1016/j.icesjms.2004.07.027.
^U. Kils (1982). "Swimming behavior, swimming performance and energy balance of Antarctic krill Euphausia superba". BIOMASS Scientific Series 3, BIOMASS Research Series: 1–122.
^S. Nicol; Y. Endo (1997). "Krill Fisheries of the World". FAO Fisheries Technical Paper. 367.
^Ratnarajah, L., Bowie, A.R., Lannuzel, D., Meiners, K.M. and Nicol, S. (2014) "The biogeochemical role of baleen whales and krill in Southern Ocean nutrient cycling". PLOS ONE, 9(12): e114067. doi:10.1371/journal.pone.0114067
^Hopkins, T.L., Ainley, D.G., Torres, J.J., Lancraft, T.M., 1993. Trophic structure in open waters of the Marginal Ice Zone in the Scotia Weddell Confluence region during spring (1983). Polar Biology 13, 389–397.
^Lancraft, T.M., Relsenbichler, K.R., Robinson, B.H., Hopkins, T.L., Torres, J.J., 2004. A krill-dominated micronekton and macrozooplankton community in Croker Passage, Antarctica with an estimate of fish predation. Deep-Sea Research II 51, 2247–2260.
^ abcGrossman, Elizabeth (14 July 2015). "Scientists consider whether krill need to be protected from human over-hunting". Public Radio International (PRI). Retrieved 1 April 2017.
^"Krill fisheries and sustainability: Antarctic krill (Euphausia superba)". Commission for the Conservation of Antarctic Marine Living Resources. 23 April 2015. Retrieved 1 April 2017.
^ abc"Krill – biology, ecology and fishing". Commission for the Conservation of Antarctic Marine Living Resources. 28 April 2015. Retrieved 1 April 2017.
^Minturn J. Wright (1987). "The Ownership of Antarctica, its Living and Mineral Resources". Journal of Law and the Environment. 4 (2): 49–78.
^S. Nicol; J. Foster (2003). "Recent trends in the fishery for Antarctic krill". Aquatic Living Resources. 16: 42–45. doi:10.1016/S0990-7440(03)00004-4.
^Josh, Gabbatiss (10 July 2018). "Krill fishing industry backs massive Antarctic ocean sanctuary to protect penguins, seals and whales". The Independent. Retrieved 10 July 2018.
^ ab"Why krill?". Southwest Fisheries Science Center, US National Oceanic and Atmospheric Administration. 22 November 2016. Retrieved 1 April 2017.
^Cheeseman MA (22 July 2011). "Krill oil: Agency Response Letter GRAS Notice No. GRN 000371". US FDA. Retrieved 3 June 2015.
^Omori, M. (1978). "Zooplankton fisheries of the world: A review". Marine Biology. 48 (3): 199–205. doi:10.1007/BF00397145. S2CID 86540101.
^Pongsetkul, Jaksuma; Benjakul, Soottawat; Sampavapol, Punnanee; Osako, Kazufumi; Faithong, Nandhsha (17 September 2014). "Chemical composition and physical properties of salted shrimp paste (Kapi) produced in Thailand". International Aquatic Research. 6 (3): 155–166. doi:10.1007/s40071-014-0076-4.
^Abe, Kenji; Suzuki, Kenji; Hashimoto, Kanehisa (1979). "Utilization of Krill as a Fish Sauce Material". Nippon Suisan Gakkaishi. 45 (8): 1013–1017. doi:10.2331/suisan.45.1013.
Boden, Brian P.; Johnson, Martin W.; Brinton, Edward: "Euphausiacea (Crustacea) of the North Pacific". Bulletin of the Scripps Institution of Oceanography. Volume 6 Number 8, 1955.
Brinton, Edward: "Euphausiids of Southeast Asian waters". Naga Report volume 4, part 5. La Jolla: University of California, Scripps Institution of Oceanography, 1975.
Conway, D. V. P.; White, R. G.; Hugues-Dit-Ciles, J.; Galienne, C. P.; Robins, D. B.: Guide to the coastal and surface zooplankton of the South-Western Indian Ocean, Order Euphausiacea, Occasional Publication of the Marine Biological Association of the United Kingdom No. 15, Plymouth, UK, 2003.
Everson, I. (ed.): Krill: biology, ecology and fisheries. Oxford, Blackwell Science; 2000. ISBN 0-632-05565-0.
Hamner, William M. (May 1984). "Krill — Untapped Bounty From the Sea?". National Geographic. Vol. 165 no. 5. pp. 626–642. ISSN 0027-9358. OCLC 643483454.
Mauchline, J.: Euphausiacea: Adults, Conseil International pour l'Exploration de la Mer, 1971. Identification sheets for adult krill with many line drawings. PDF file, 2 Mb.
Mauchline, J.: Euphausiacea: Larvae, Conseil International pour l'Exploration de la Mer, 1971. Identification sheets for larval stages of krill with many line drawings. PDF file, 3 Mb.
Tett, P.: The biology of Euphausiids, lecture notes from a 2003 course in Marine Biology from Napier University.
Tett, P.: Bioluminescence, lecture notes from the 1999/2000 edition of that same course.